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Localised sunshade could stop Arctic melting

By Michael Marshall

IF WE have to hack the planet, we could at least do it with some finesse. A rough modelling study offers a crude blueprint for how targeted geoengineering could preserve the Arctic ice cap, but raises questions about who decides which areas to save.

In a bid to reduce these trade-offs, Douglas MacMartin of the California Institute of Technology and colleagues simulated a more regional approach. They set up a simple climate model in which CO2 levels were doubled, which is expected to happen in the second half of this century.

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Next they modelled three geoengineering scenarios&colon; a uniform global sunshade, one sunshade over each pole, and a whole-planet sunshade that was thickest over the North Pole and thinned as it spread southwards. They also varied the time of year the sunshades were up.

The team found that the regional geoengineering approaches gave better results. A uniform global sunshade left some regions sweltering and others too cold. Regional solutions reduced the disparities.

To see if it was possible to stop the Arctic sea ice from melting, MacMartin tried switching a sunshade on above the Arctic during summers only. He found this could restore the Arctic sea ice to its preindustrial extent, while also bringing average global temperatures and rainfall close to their original levels (Nature Climate Change, doi.org/jkh).

Tim Lenton of the University of Exeter, UK, says that current climate models are not good enough to draw such conclusions. He is particularly sceptical about the claims for restoring Arctic sea ice, as the model MacMartin used distorts the geography of the North Atlantic to simplify its calculations.

MacMartin admits that his simulations are “idealised”, but says his results open the way for a more sophisticated form of geoengineering. By combining different techniques, it may be possible to tailor the future climates of different continents.

Lenton points out that nations would then have to decide between them which aspects of the global climate to preserve. “Is protecting the sea ice more important than protecting the Indian monsoon?” he says. “Who decides? It inevitably turns into a power game.”